PROJECT SUMMARY/ABSTRACT The goal of this project is to examine the role of p52, one of the five nuclear factor-kB (NF-kB) subunits, in regulating mesenchymal (MES) transformation in glioblastoma (GBM). GBM is the most common primary glial neoplasm in adults and, despite aggressive multimodal therapy, is nearly universally fatal. The classification of GBM into molecular subtypes based on gene expression profiles has revealed several regulatory pathways critical to GBM pathogenesis. Recently, NF-kB was identified as a master regulator of the highly aggressive MES GBM subtype. The central hypothesis of our work is that p52 induces MES transformation in GBM and that modulation of this p52-specific pathway alters the tumor microenvironment (TME) and affects the efficacy of anti-GBM therapy. Our aims examine sequential aspects of the mechanism by which p52 directs subtype differentiation to uncover novel strategies to improve the treatment of this devastating disease. In Aim 1, we examine the effects of p52 modulation on subtype transformation. Another known master regulator of MES differentiation, Stat3, plays a critical role in promoting p52 formation. We will examine the hypothesis that Stat3-mediated MES differentiation occurs through regulation of p52 production. Additionally, as NF-kB is a transcription factor that modulates gene expression, we will examine the downstream profile affected by differential p52 promoter binding through genome-wide target-identification to elucidate potential targets critical to MES transformation. As transformation between subtypes is dependent not only on cell-intrinsic signaling pathways, but also on cell-extrinsic changes, in Aim 2 we will investigate the impact of modulating p52 on the TME and on GBM treatment efficacy. Specifically, we will alter p52 expression in an immunocompetent murine GBM model and test the hypothesis that p52 modulation alters the TME and affects the response to adjuvant therapy. These complimentary aims will define the role of p52 in MES transformation in GBM. From a broader perspective, the results of the current project will expand our understanding of GBM molecular subclass transformation and potentially lead to the identification of novel targets that can enhance anti-GBM therapy and improve patient survival.